Nowadays, in relation to health effects of smoking, a technique for reducing a harmful component in cigarette smoke is demanded in the cigarette field. Cigarette smoke contains various harmful components. Above all, an aldehyde compound such as formaldehyde not only has a pungent odor but also is noticed as an allergen. However, it is different to remove the aldehyde compound by adsorption with a general-purpose cigarette filter. In order to adsorb the harmful substance, an activated carbon is widely used conventionally. For example, Japanese Application Laid-Open No. 2009-519034 publication (JP-2009-519034A, Patent Document 1) discloses a cigarette filter comprising a mouth end, an activated carbon, and a sodium bicarbonate-treated fiber located between the activated carbon and the mouth end.
However, physical adsorption, typically using an activated carbon, removes not only the harmful substance but also a palatable component in cigarette smoke. In other words, removal of nicotine, tar, and other flavor components changes the taste of cigarette smoke, so that a feeling of satisfaction in smoking is inhibited. Thus, a method for selectively adsorbing an aldehyde compound from mainstream cigarette smoke is desired.
In this respect, as a cigarette which can selectively remove formaldehyde in mainstream smoke, Japanese Patent No. 3895327 publication (JP-3895327B, Patent Document 2) discloses a cigarette comprising a tobacco rod and 48.3 to 146.7 mg of a hydrotalcite compound connected to the tobacco rod. This document also discloses that a paper sheet comprising a particulate hydrotalcite compound having an average particle size of not more than 10 μm is formed to produce a cigarette.
However, in the cigarette, the particulate hydrotalcite compound is easily eliminated and scattered.
On the other hand, as a method for removing a harmful component using an organic component, WO2009/031248 publication (Patent Document 3) discloses a composition comprising at least one amino compound selected from the group consisting of an amino acid and an aminosulfonic acid and a silica gel, and a cigarette filter comprising the composition. This document also discloses that the filter has a triplet structure in which a gap in a divided filter is filled with the composition.
However, since this composition contains the silica gel, the taste of the cigarette is significantly changed. Moreover, use of a plasticizer (e.g., triacetin) in a filter comprising a cellulose acetate tow decreases a capacity to adsorb formaldehyde. Further, since the filter has a triplet structure, damage to the filter involves a risk of getting a scattered particulate porous material in the eyes or the lungs. Moreover, the triplet structure cannot improve the hardness of the filter.
Japanese Patent Application Laid-Open No. 2007-319041 publication (JP-2007-319041A, Patent Document 4) discloses a cigarette filter material in which at least part of a support comprising a filament aggregate is coated with an amino acid or a salt thereof. According to this document, the cigarette filter material is produced by treating a support with a solution at least containing an amino acid or a salt thereof and a polar solvent.
However, since the support for holding an amino acid or a salt thereof in this cigarette filter material is in the form of a tow, the method for producing the cigarette filter is limited.
Japanese Patent Application No. 10-215844 publication (JP-10-215844A, Patent Document 5) discloses a cigarette filter which comprises a tow comprising a filter component, and a water-soluble fibrous resin contained in the tow to bond the filter component. This document also discloses that the filter component is in the form of a particulate or a fiber and that a particulate filter component is used in combination with a fibrous filter component in order to form a tow.
However, this cigarette filter cannot reduce the amount of formaldehyde sufficiently. Further, the document is silent on detailed combination of the particulate filter with the fibrous filter and discloses in Examples that a water-soluble hot-melt resin is added to a cellulose acetate tow.
Japanese Patent No. 3905886 publication (JP-3905886B, Patent Document 6) discloses a cigarette containing a basic amino acid or a salt thereof selected from the group consisting of lysine, histidine, ornithine, citrulline, hydroxyzine, and a salt thereof in an amount of 1 to 27.6 mg/cigarette. According to this document, an aqueous solution of the basic amino acid or the salt thereof is added to a filter.
However, since the cigarette contains water due to the addition of the liquid substance to the filter, the liquid substance is scattered or moved to a tobacco leaf to leave a spot on the leaf during cigarette storage.    [Patent Document 1] JP-2009-519034A (claim 1)    [Patent Document 2] JP-3895327B (Claims and Background Art)    [Patent Document 3] WO2009/031248 (Claims, Paragraph and Examples)    [Patent Document 4] JP-2007-319041A (Claims)    [Patent Document 5] JP-10-215844A (Claim 1, Paragraphs and [0014], and Examples)    [Patent Document 6] JP-3905886B (Claims)